Which one of the following is used in preparing a natural mosquito repellent?

Answer: C. LEMONGRASS is used in preparing a natural mosquito repellent. LEMONGRASS (Cymbopogon citratus, C. flexuosus, and related species) contains aromatic essential oils, primarily CITRAL (about 70-80% of the oil), GERANIOL, and CITRONELLAL. These compounds give lemongrass its strong citrus-like aroma that MOSQUITOES FIND REPELLENT. CITRONELLA OIL, extracted from a related species CYMBOPOGON NARDUS, is the most well-known natural mosquito repellent in commercial use — found in candles, sprays, lotions, and oils. Lemongrass and citronella are closely related and share active repellent compounds (citral/citronellal). India is the world's largest producer of lemongrass oil. Mechanism: the volatile compounds mask the human scent cues (CO2, lactic acid, body heat) that mosquitoes use to locate hosts, AND they directly irritate mosquito antennal receptors. Distractors: (A) CONGRESS GRASS (Parthenium hysterophorus) is an invasive weed and allergen, NOT a mosquito repellent — it CAUSES dermatitis and respiratory problems. (B) ELEPHANT GRASS (Pennisetum purpureum) is a fodder grass for livestock and biofuel; NOT a known mosquito repellent. (D) NUT GRASS (Cyperus rotundus) has Ayurvedic medicinal uses (gastric, anti-inflammatory) but is NOT a known mosquito repellent. Source: NCERT Class 12 Biology — applied botany / CSIR-Central Institute of Medicinal and Aromatic Plants.